Based on our years of experience testing VPNs for privacy, usability and speed, these are the most important factors to consider when purchasing a fast VPN:

Speed

If you're looking for the fastest VPN, then speed will naturally be your top consideration. There are a lot of VPNs that struggle with speeds and can slow your internet by 50% or more. Look for a VPN that drops your speed by only about 20% or less.

Privacy

Privacy is a major consideration for any VPN, regardless of its speed performance. The VPNs we've highlighted above all deliver top-notch privacy paired with fast speeds, so you'll get the best of both worlds with any of our recommended options. Look for basic privacy protections like a kill switch, DNS leak protection and a no-logs policy (preferably audited and/or tested in the wild). Other privacy features to look out for include obfuscation, multi-hop connections and Tor over VPN.

Protocols

Some VPN protocols can deliver faster speeds than others. We recommend using the OpenVPN protocol for the best combination of speed and security. If you want to get the most speed out of your VPN, then you can use a lightweight protocol like WireGuard or your VPN provider's proprietary (usually WireGuard-based) VPN protocol.

Server network

You'll want a VPN service with a large network of servers worldwide. This will help ensure that you'll have access to fast, stable VPN connections wherever you may be located. Generally, around 75 server locations and above is a decent network. Some VPNs even have servers in 100 or more countries. The main thing you'll want in your VPN's network is servers located near where you are or where you plan on traveling. If a VPN only has servers in 50 countries, but covers all of the regions you plan on using, then its server network should suffice. 

Cost

If you're on a budget, then the overall value of your VPN will be a major consideration. If you want the largest savings, opt for a yearly plan, which will generally afford you better value over time than going month-to-month. A budget-friendly VPN can cost about $40 to $60 per year, while a more expensive VPN can run you upwards of $100 per year.